1. Field of the Invention
This invention relates to the field of wireless communication systems. More specifically, the present invention relates to dynamically switching between speech coders.
2. Background
The use of wireless communication systems is growing with users now numbering well into the millions. One of the most popular wireless communications systems is the cellular telephone, consisting of a mobile unit (or handset) and a base station. Cellular telephones allow a user to talk over the telephone without having to remain in a fixed location. This allows users to, for example, move freely about the community while talking on the phone. However, one inconvenience associated with routine use of a cellular telephone is the constant need to recharge and replace depleted batteries in the handset.
One important service offered by wireless communication systems is speech transmission. In many analog communication systems, the voice signal is modulated and transmitted on a radio frequency carrier. In conventional digital communication systems, the voice data is typically converted to a binary bit stream and compressed prior to transmission. Converting voice data to a compressed binary stream of data consumes both battery power and processor power.
A codec is a device which transforms the voice into a digital stream of data suitable for transmission over a radio interface. Current digital wireless communications systems typically use what is called a bit-exact speech coder and decoder. Bit-exact speech coders output an exact sequence of output bits for each input signal. The predictability of the output maintains a high signal quality during the coding process. While bit-exact speech coders ensure reliable voice transmission, they do so at the expense of battery power and processor power.
Improvements in battery technology, while helpful, have not avoided the seemingly ever-present need to recharge and replace mobile unit batteries. What is needed is a system to further conserve battery power by reducing the power consumed by the mobile unit.
Moreover, wireless communications systems are becoming increasingly complex with the user having a large number of service features, such as call waiting, call forwarding, caller identification, and conference calling. While these features are desirable to the user, each active feature consumes processor power. What is needed is a system to further conserve processor power by reducing the processor usage by the mobile unit.